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Molecular Gas in the Outskirts

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Outskirts of Galaxies

Part of the book series: Astrophysics and Space Science Library ((ASSL,volume 434))

Abstract

The outskirts of galaxies offer extreme environments where we can test our understanding of the formation, evolution and destruction of molecules and their relationship with star formation and galaxy evolution. We review the basic equations that are used in normal environments to estimate physical parameters like the molecular gas mass from CO line emission and dust continuum emission. Then we discuss how those estimates may be affected when applied to the outskirts, where the average gas density, metallicity, stellar radiation field and temperature may be lower. We focus on observations of molecular gas in the outskirts of the Milky Way, extragalactic disk galaxies, early-type galaxies, groups and clusters. The scientific results show the versatility of molecular gas, as it has been used to trace Milky Way spiral arms out to a galactocentric radius of 15 kpc, to study star formation in extended ultraviolet disk galaxies, to probe galaxy interactions in polar-ring S0 galaxies and to investigate ram pressure stripping in clusters. Throughout the chapter, we highlight the physical stimuli that accelerate the formation of molecular gas, including internal processes such as spiral arm compression and external processes such as interactions.

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Acknowledgements

We are grateful to Françoise Combes, Jennifer Donovan Meyer, Natsuko Izumi, and Hiroyuki Nakanishi for their advice, reading suggestions, and comments. We also thank Natsuko Izumi for allowing us to use her figure for the distribution of molecular clouds in the outer MW (Fig. 6.4). JK thanks the NAOJ Chile observatory, a branch of the National Astronomical Observatory of Japan, and the Joint ALMA Observatory for hospitality during his sabbatical visit. JK acknowledges the support from NASA through grant NNX14AF74G.

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  1. European Southern Observatory, Alonso de Córdova 3107, Vitacura, Casilla, 19001, Santiago, Chile

    Linda C. Watson

  2. NAOJ Chile Observatory, Joaquín Montero 3000, Oficina 702, Vitacura, Santiago, Chile

    Jin Koda

  3. Joint ALMA Office, Alonso de Córdova 3107, Casilla 19001, Vitacura, Santiago, Chile

    Jin Koda

  4. Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY, 11794, USA

    Jin Koda

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  1. Inst de Astrofísica de Canarias, San Cristobal de la Laguna, Spain

    Johan H. Knapen

  2. Space Telescope Science Institute, Baltimore, USA

    Janice C. Lee

  3. Dept. Astrofisica, Universidad Complutense de Madrid, Madrid, Spain

    Armando Gil de Paz

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Watson, L.C., Koda, J. (2017). Molecular Gas in the Outskirts. In: Knapen, J., Lee, J., Gil de Paz, A. (eds) Outskirts of Galaxies. Astrophysics and Space Science Library, vol 434. Springer, Cham. https://doi.org/10.1007/978-3-319-56570-5_6

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